The present exemplary embodiment relates to a scheduling system. It finds particular application in conjunction with scheduling print jobs for improving the reliability of a printing system and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
Electronic printing systems typically employ a scanner for scanning image-bearing documents and conversion electronics for converting the image to image signals or pixels. The signals are stored and are read out successively to a printer for formation of the images on photoconductive output media such as a photoreceptor. When multiple jobs are to be sequentially printed, a process known as “job streaming” is commonly implemented. Job streaming is the ability of a printer system to complete successive printing jobs with a minimum of delay time between jobs. A control system associated with the image output terminal (IOT) of the machine identifies that multiple jobs have been scheduled, determines their characteristics and determines the necessary delay between jobs. In some cases, the control system will enable a second job to begin printing prior to completion of the first job.
U.S. Pat. No. 6,618,167 to Shah, the disclosure of which is incorporated herein by reference, provides a scheduling scheme to improve the productivity of printers, particularly color printers. The scheduling scheme accounts for difference in the rasterization execution time of some print jobs.
U.S. Pat. No. 5,095,369 to Ortiz, et al., incorporated herein by reference, discloses a method for enhancing productivity in an electronic printer incorporating finishing activities and operating in a job streaming mode. Printing and collating of sets of original scanned documents are controlled so that collated sets are successively presented by the printer to the finisher nearly coincident with conclusion of the finishing activity being accomplished for a current job. The system uses a predictive algorithm which is used to increase reliability of printer components by cycling down the printer between jobs in situations where the finishing activity for a current job requires an extraordinarily long time to complete compared with the cycle down/cycle up time of the printer.
Printing systems now being developed may employ multiple print engines for black, process (or full) color, and custom color (single color or monochrome) printing of selected pages within a print job. The following references, the disclosures of which are incorporated by reference in their entireties, variously relating to what have been variously called “tandem engine” printers, “parallel” printers, or “cluster printing” (in which an electronic print job may be split up for distributed higher productivity printing by different printers, such as separate printing of the color and monochrome pages), and “output merger” or “interposer” systems: U.S. Pat. No. 5,568,246 to Keller, et al., U.S. Pat. No. 4,587,532 to Asano, U.S. Pat. No. 5,570,172 to Acquaviva, U.S. Pat. No. 5,596,416 to Barry, et al.; U.S. Pat. No. 5,995,721 to Rourke et al; U.S. Pat. No. 4,579,446 to Fujino; U.S. Pat. No. 5,389,969 to to Soler, et al.; a 1991 “Xerox Disclosure Journal” publication of November-December 1991, Vol. 16, No. 6, pp. 381-383 by Paul F. Morgan; and a Xerox Aug. 3, 2001 “TAX” publication product announcement entitled “Cluster Printing Solution Announced.”
Intermittent use of xerographic printers, characterized by relatively frequent on-off cycles has been shown, statistically, to lead to lower reliability. As with the operation of a car, startup and stopping are much more stressful than constant operation. Using a printer casually for relatively short jobs is much more stressful, as measured by maintenance costs per page, than running the same printer more continuously.